Effect of Iron Ions on the Crystal Growth Kinetics and Microstructure of Calcium Carbonate

In the present work, calcium carbonate was precipitated at 28 °C in the presence of iron ions using an accelerated scale method based on CO2 repelling from the solution. The polymorphism and morphology of the obtained precipitates were investigated using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared analyses. At high solution supersaturations, iron ions did not have a significant effect on the inhibition of calcium carbonate crystallization. However, at relatively low solution supersaturations, iron ions addition retards the nucleation of calcium carbonate. Past the onset of nucleation, iron ions increased the CaCO3 growth rate, and most of calcium carbonate amounts precipitated in the bulk solution rather than on the cell walls, decreasing, therefore, risks of scaling. The inhibiting effectiveness of iron ions was explained by a three-step calcium carbonate formation mechanism involving calcium carbonate interaction with siderite.